Multiprotocol label switching (MPLS) is a scheme in high-performance telecommunication networks which directs and carries data from one node to the next node. The multiprotocol label switching mechanism assigns labels to data packets. Packet forwarding decisions from one node to the next node are made solely on the contents of the label for each data packet, without the need to examine the data packet itself.
Generalized Multiprotocol Label Switching (GMPLS) is a type of protocol which extends multiprotocol label switching to encompass network schemes based upon time-division multiplexing (e.g. SONET/SDH, PDH, G.709), wavelength multiplexing, and spatial multiplexing (e.g. incoming port or fiber to outgoing port or fiber). Multiplexing, such as time-division multiplexing is when 2 or more signals or bit streams are transferred simultaneously. In particular, time-division multiplexing (TDM) is a type of digital multiplexing in which 2 or more signals or bit streams are transferred simultaneously as sub-channels in one communication channel, but are physically taking turns on the communication channel. The time domain is divided into several recurrent timeslots of fixed length, one for each sub-channel. After the last sub-channel, the cycle starts all over again. Time-division multiplexing is commonly used for circuit mode communication with a fixed number of channels and constant bandwidth per channel. Time-division multiplexing differs from statistical multiplexing, such as packet switching, in that the timeslots are returned in a fixed order and preallocated to the channels, rather than scheduled on a packet by packet basis.
The optical transport hierarchy (OTH) supports the operation and management aspects of optical networks of various architectures, e.g., point-to-point, ring and mesh architectures. One part of the optical transport hierarchy is a multiplex hierarchy, which is a hierarchy consisting of an ordered repetition of tandem digital multiplexers that produce signals of successively higher data rates at each level of the hierarchy. Shown in FIG. 1 is an exemplary multiplexing hierarchy specified by way of optical channel data units, i.e., ODUj, where j varies from 0 to 4; and optical channel transport units, i.e., OTUk, where k varies from 1 to 4. The optical channel data units refer to a frame format for transmitting data which can be either fixed in the amount of data and data rate or variable in the amount of data and/or data rate.
Examples of optical channel data units that are fixed in the amount of data and data rate include those specified by ODU0, ODU1, ODU2, ODU3, and ODU4. An example of an optical channel data unit that is variable in the amount of data and/or data rate is referred to in the art as ODUflex
One of the properties of the multiplexing hierarchy is that while the data rate changes over the different levels in the multiplexing hierarchy, the frame format remains identical. An ODU0 frame format 10 shown in FIG. 2. Like all other ODUjs, the ODU0 frame format 10 consists of a structure of four rows and 3824 columns, as presented in FIG. 2. The ODU0 frame format 10 is further divided into an ODUk overhead area 12 (the first fourteen columns) and an optical channel payload unit (OPU) area 14. The optical channel payload unit area 14 contains two columns of overhead and 3808 columns of payload area which is available for the mapping of client data.
The nominal ODU0 rate equals half the optical channel payload unit area 14 rate of an ODU1. The latter is tailored for transport of STM-16/OC-48 signals at 2,488.32 Mbit/s. The ODU0 rate is 1,244.16 Mbit/s±20 ppm, while the rate of the available OPU0 payload area is 1,238.95431 Mbit/s.
Shown in FIG. 3 is a frame format 16 having two ODU0s multiplexed into an ODU1. The payload area of ODU1 frame format 16 of the latter has been divided into two time slots called optical channel tributary unit (or slots) 0 and 1 (ODTU01). As shown in FIG. 3, each ODU0 is mapped into an ODTU01 time slot using a procedure known in the art as asynchronous mapping procedure (AMP), which is consistent with the legacy mapping of ODUj into ODUk.
The optical channel data units within the multiplexing hierarchy are referred to in the art as lower order or higher order. A higher order optical channel data unit refers to a server layer to which a lower order optical channel data unit (client layer) is mapped to. Optical channel data units include a parameter referred to as tributary slot granularity which refers to a data rate of the timeslots within the optical channel data unit. The tributary slot granularity of optical channel data units include time slots of approximately 2.5 Gbit/s. OPUk (when k=1, 2, 3, 4) is divided into equal sized Tributary Slots or Time Slots of granularity (1.25 G or 2.5 G) to allow mapping of lower order ODUj (where j<k). For example: On OPU4, there are 80 (1.25 G) Tributary Slots. To map: ODU3 into OPU4=>31 TSs are used; ODU2/2e into OPU4=>8 TS are used; ODU1 into OPU4=>2 TSs are used; and ODU0 into OPU4 =>1 TS is used.
ODTUG refers to grouping of Tributary Slots that facilitates mapping of any ODUj into ODUk. ODTUjk refers to Optical Channel Tributary Unit j into k. This defines Tributary Slot grouping for mapping ODUj into ODUk. In particular, OPU2 and OPU3 support two tributary slot granularities: (i) 1.25 Gbps and (ii) 2.5 Gbps. Information indicative of tributary slot granularity can be encoded into the overhead of the ODUj optical channel data unit.
The current version of ITU-T G.709 (12/2009) of the generalized multiprotocol label switching supports “multi-stage ODU multiplexing”, which refers to the multiplexing of lower order ODUj into higher order ODUk. The multistage ODU multiplexing can be heterogeneous (meaning lower order ODUj of different rates can be multiplex into a higher order ODUk).
Optical transport networks support switching at two layers: (i) ODU Layer, i.e., time division multiplexing and (ii) OCH Layer—Lambda or wavelength switching where OCH stands for Optical Channel. The nodes on the optical transport network may support one or both the switching types. When multiple switching types are supported Multi-Layer Network (MLN) based routing [RFC5339] is assumed.
Generalized Multiprotocol Label Switching includes multiple types of optical channel data unit label switched paths including protection and recovery mechanisms which specifies predefined (1) working connections within a shared mesh network having multiple nodes and communication links for transmitting data between the nodes; and (2) protecting connections specifying a different group of nodes and/or communication links for transmitting data in the event that one or more of the working connections fail. Data is initially transmitted over the optical channel data unit label switched path referred to as a working connection and then when a working connection fails, the Generalized Multiprotocol Label Switching protocol automatically activates one of the protecting connections for redirecting data within the shared mesh network.
However, the mechanisms defined in GMPLS for setting up the optical channel data unit label switched paths have overlooked a number of issues related to the multiplexing hierarchy. In particular, the present mechanisms defined in GMPLS define a separate optical channel data unit label switched path with reserved timeslots for each multiplexing level within the multiplexing hierarchy. This increases the size of databases stored by the nodes for managing the optical channel data unit label switched paths, and increases the amount of signaling between the nodes to set up the increased number of optical channel data unit label switched paths.
The presently disclosed and claimed inventive concepts support multi-stage multiplexing on an optical channel data unit label switched path to reduce the described drawbacks of the conventional GMPLS system.